Not long ago, answering a query meant traveling to the reference desk of your local library. Today, search engines enable us to access immense quantities of useful information in an instant, without leaving home. Tools like email, online books and photos, and video chat all increase productivity while decreasing our reliance on car trips, pulp and paper.

But as computers become a bigger part of more people's lives, information technology consumes an increasing amount of energy, and Google takes this impact seriously. That's why we have designed and built the most energy efficient data centers in the world, which means the energy used per Google search is minimal. In fact, in the time it takes to do a Google search, your own personal computer will use more energy than Google uses to answer your query.

Recently, though, others have used much higher estimates, claiming that a typical search uses "half the energy as boiling a kettle of water" and produces 7 grams of CO2. We thought it would be helpful to explain why this number is *many* times too high. Google is fast — a typical search returns results in less than 0.2 seconds. Queries vary in degree of difficulty, but for the average query, the servers it touches each work on it for just a few thousandths of a second. Together with other work performed before your search even starts (such as building the search index) this amounts to 0.0003 kWh of energy per search, or 1 kJ. For comparison, the average adult needs about 8000 kJ a day of energy from food, so a Google search uses just about the same amount of energy that your body burns in ten seconds.

In terms of greenhouse gases, one Google search is equivalent to about 0.2 grams of CO2. The current EU standard for tailpipe emissions calls for 140 grams of CO2 per kilometer driven, but most cars don't reach that level yet. Thus, the average car driven for one kilometer (0.6 miles for those in the U.S.) produces as many greenhouse gases as a thousand Google searches.

We've made great strides to reduce the energy used by our data centers, but we still want clean and affordable sources of electricity for the power that we do use. In 2008 our philanthropic arm, Google.org, invested $45 million in breakthrough clean energy technologies. And last summer, as part of our Renewable Energy Cheaper than Coal initiative (RE<C), we created an internal engineering group dedicated to exploring clean energy.

We're also working with other members of the IT community to improve efficiency on a broader scale. In 2007 we co-founded the Climate Savers Computing Initiative, a group which champions more efficient computing. This non-profit consortium is committed to cutting the energy consumed by computers in half by 2010 — reducing global CO2 emissions by 54 million tons per year. That's a lot of kettles of tea.

Update on 1/12 @ 4 PM:Harvard professor Alex Wissner-Gross provided new details on his energy research, in a TechNewsWorld article.

Update on 1/16 @ 1 PM: The Sunday Times clarified its article on the energy consumed by a Google search, accepting our calculation that a single search accounts for about 0.2g of carbon. That means a typical individual's Google use for an entire year would produce about the same amount of CO2 as just a single load of washing.